DAVENPORT, Iowa/MARSHALLTOWN, Iowa, Jan 12 (Reuters) - A rare sign of discord emerged on Sunday between progressive Democratic presidential contenders Elizabeth Warren and Bernie Sanders over a report that Sanders' campaign volunteers had called her a candidate of the elite in conversations with voters.

"I was disappointed to hear that Bernie is sending his volunteers out to trash me," Warren told reporters after a campaign event in Marshalltown, Iowa, which will hold the nation's first nominating contest on Feb. 3.

"I hope Bernie reconsiders and turns his campaign in a different direction."

Warren and Sanders, who are friends, fellow U.S. senators and their party's progressive standard-bearers, agreed early in the nominating contest to an informal non-aggression pact and have largely avoided criticizing each other.

Politico reported late on Saturday that Sanders' campaign had distributed talking points for volunteers on what to say to voters who are thinking of supporting his main rivals - former Vice President Joe Biden, Pete Buttigieg, the former mayor of South Bend, Indiana, and Warren.

The guidance suggested that volunteers argue Warren was supported by "highly-educated, more affluent people who are going to show up and vote Democratic no matter what," rather than motivating people who do not normally vote, Politico reported. Reuters could not verify the talking points.

Sanders said on Sunday he did not approve the negative talking points about other candidates.

"We have over 500 people on our campaign. People do certain things. I'm sure that on Elizabeth's campaign people do certain things as well," Sanders told reporters after a rally in Iowa.

"But you've heard me for months, I have never said a negative word about Elizabeth Warren, who is a friend of mine. We have differences on issues. That's what a campaign is about."

REFRAINING FROM ATTACKS

The spat underscores the rising stakes for Warren, Sanders and the 11 other Democrats seeking their party's nod to take on Republican President Donald Trump in November's election.

The latest Iowa opinion polls show Sanders with a narrow lead in the state. He has sought to cast himself as the only one capable of beating Trump, arguing he would drive turnout among working-class and minority voters who would not otherwise vote.

Sanders supporters have also been increasingly targeting Biden in recent weeks. Biden trails Sanders in early nominating states but leads him in most national opinion polls among Democrats.

In a statement on Saturday, Sanders campaign senior adviser Jeff Weaver said it was "appalling" that Biden and former Secretary of State John Kerry, a Biden supporter, had attempted to defend Biden's 2002 vote as a U.S. senator for the use of force in Iraq.

Sanders, who opposes military interventions and has warned that Trump is leading the United States to war with Iran, has criticized Biden for supporting the Iraq war.

Warren - who has criticized Biden and Buttigieg for their ties to wealthy donors - said on Sunday that Democrats could ill afford to repeat 2016, when bad blood between supporters of Sanders and the eventual nominee, Hillary Clinton, hurt the party's campaign against Trump.

"Democrats want to win in 2020," she said. "We all saw the impact of the factionalism in 2016, and we can't have a repeat of that." (Reporting by Simon Lewis and Joseph Ax; Editing by Soyoung Kim and Peter Cooney)